Patent GB-294715-A (GB)
Title: Improvements in and relating to double-current cable code telegraphy
IPC: H04L25/20
Filed: 1927-05-05
Abstract: 294,715. Higgitt, H. V., and Eastern Telegraph Co., Ltd. May 5, 1927. Systems using code elements and spaces distinguished by polarity and duration of current; repeating-systems using contact-making relays, automatic telegraphs; siphon recorders. - Dashes, dots and spaces may be represented, in any desired assignments, by signal-elements each made up of two halfelements of marking or spacing current, four such signal-elements, viz., (+ +), (+ -), (- +), (- -), being available. Specification 267,180 describes a system in which a dot is represented by (+ -), a dash by (+ +), and a space by (- -). According to the present invention any other assignment of the available signals may be adopted; thus in the example illustrated, a dot is represented by (+ +), a dash by (- -), and a space by (+ -), as shown in Fig. 1. Specification 275,538, according to which a dot is represented by (+ -), is referred to. Transmitter. Fig. 5 shows means whereby signals of the type described are sent to line under the control of a tape punched according to the ordinary cable code, the lever a being set to b for a dash to c for a dot, and to the middle position for a space, under the control of the tapeoperated mechanism described in Specification 26278/13. The cam d revolves once per signal element, and when a dash is being signalled the magnet f is energized so that the piece h is raised when the hammer e is driven to the left by the cam. The lever j therefore remains in the position shown throughout the duration of the signal element, the current to line L taking the form (- -). When a space is being signalled neither of the magnets f, g, is energized : the piece h is therefore driven forward by the hammer e and cam d for half a revolution, and withdrawn by the springs z for the second half : the lever j therefore moves to the left and back so as to cause the emission of a signal element of the form (+ -). If a dot is being signalled the magnet g is energized : both the pieces h, k, are therefore driven forward bv the hammer e and cam d. The pieces h, k return during the second half of the revolution of the cam, but the lever j is retained in the left-hand position by a latch m of the kind described in Specification 234,179 which engages an intermediate lever n until tripped by the tail o of the cam: a signal element of the form (+ +) is consequently sent to line L by the lever j. Receiver. Signals produced as above are translated by the apparatus shown in Fig. 6 into ordinary cable-code settings of the dot contact w and dash contact v. Thus. when a dot signal element (+ +) is received by the line magnet R the piece t remains up and is missed by the hammer s, while the piece x is drawn down by the magnet q throughout the duration of the element : the piece x is therefore thrust forward by the cam projection r, so as to close the dot contact w, during the last quarter of the signal element. During the receipt of a space signal (+ -) the piece t remains up during the first half-element so that the hammer passes beneath it when driven by the part y of the cam, and it merely rests on the top of the hammer when the second half-element arrives, at the same time the piece x, although drawn down by the magnet q during the first half-element, does not close the contact w, since the part y of the cam is not deeper than the gap between the hammer s and piece x, while during the second half-element the piece x rises and is missed by the hammer s; thus neither of the contacts v, w, is actuated by a space element. When a dash (- -) is received the piece x remains in the upper position and is missed by the hammer s, while the piece t is thrust forward by the cam projection r so as to close the contact v during the last quarter of the element. The duration of the contacts made at v and w may be determined by latching- devices as described in Specification 234,179. The contact levers may, however, be replaced by perforating-mecha,nism as described in Specification 28952/13. Signals of the kind described may be received on a siphon recorder, dots and dashes being indicated by marks above and below the line, provided that the moving parts of the recorder have sufficient inertia to suppress the space signals (+ -). Distortion due to a final dot being followed by a, space (+ + + -) may be reduced by inclining the siphon to the direction of movement of the paper so that dashes are recorded somewhat later than dots.